1. Field of the invention
The present invention relates to a method and an apparatus for removing a coated film from the surface of a bumper of an automobile to reuse the bumper. Particularly, the present invention relates to a method and an apparatus for removing a coated film from the surface of a bumper of an automobile, in which a high pressure water or a heated high pressure air is spouted onto the bumper, thereby easily removing the coated film.
2. Description of the Prior Art
Recently, the environmental problems and the resource recycling problems are called to the attention, and regeneration of products is being briskly discussed.
For example, the technique of recycling the defective resin products such as bumpers and side molding products and recycling the resin products of disused cars is recognized as being important.
In many cases, the resin products such as bumpers and side molding products are painted for improving the aesthetic appearance.
For example, the bumper is made of a thermoplastic resin such as a polypropylene resin, and its surface is coated.
The coating is done by using a thermosetting resin selected from a group consisting of amino-polyester resin, amino acrylic resin, polyester urethanic resin, acryl urethanic resin, polyester melanic resin, and acrylmelanic resin. Before the hardening reaction, these resins are in the liquid phase, but when they have gone through the coating process, they have bridge structures.
They have strong and dense structures, and therefore, after the coating, they become anti-chemical, thermally resistant, scratch-resistant, weather resistant, and shiny.
For example, in most vehicles, the base stock of the bumper is 2.5-5 mm-thick, and thereon, a coating of 15-30 microns is done by using polyester urethanic resin, this being the general practice.
In another method, the base stock is a thermoplastic resin, and thereon, an inorganic compound is coated.
When recycling such a coated bumper, if the bumper is crushed without removing the coated layer so as to form into pellets, then the coated layer material is mixed into the polypropylenic resin of the bumper base stock material. In this state, if the polypropylenic resin is molded, the coated layer material impedes the fluidizing of the melted resin, or forms bubbles and weld marks, thereby causing molding defects. Further, the aesthetics of the bumper is aggravated.
Further, there is no melting compatibility between the base resin and the coated layer material, and therefore, the homogeneity lacks, with the result that the mechanical strength of the bumper material is aggravated.
Accordingly, if a bumper is to be recycled, the removal of the coated layer has to be necessarily preceded.
The conventional coated layer removing method includes mechanical methods and chemical methods. First the mechanical methods will be briefly described.
Japanese Patent 95-164444 (entitled "METHOD AND APPARATUS FOR RECOVERING AND ASSEMBLING WASTE MOLDING PRODUCTS") discloses the following technique. That is, a coated resin molding product is crushed into small pieces, and they are ground by using a surface grinder so as to peel off the coated layer. Then a compression impact force and an impact abrasion force are applied to detach the peeled coated layer. This method is a vibration-compression method, and is known to be very effective in this field.
However, in this method, the treating process is very complicated, to such a degree that the whole process consists of 6-8 steps. Depending on the kind of the coated resin products, the whole process has to be repeated for several times, and in spite of this, only 90% of the coated layer can be removed. Therefore, the required time period is very much extended. Further, the coated layer peeling facility requires a large installation area, and the process steps have to be repeated, with the result that the operating cost is increased.
As another mechanical peeling method, there is British Patent 94-2278119A (entitled "RECYCLING OF RESIN COMPOSITIONS"). In this method, a coated resin molded product is crushed and extruded, and extended by using a roll. Then a recrushing is carried out.
This method has the advantage that the process is relatively simple. However, the extruded sheet is mixed with the pieces of the coated layer, and the peeling efficiency is also low.
As similar techniques, there are Japanese Patent 95-256640 and 95-256641. In these techniques, only a rolling is carried out to extend the coated resin product, thereby peeling the coated layer. However, this technique is not suitable for products of complicated contours such as the bumpers of automobiles.
In another mechanical method, tiny grinding particles are spouted loaded in a compressed air to remove the coated layer, this being a shot-blast method. In this method, the frictions and impacts are utilized to remove the coated layer, and therefore, the non-toxicity and the environmental stability are its merits. However, the treating time is extended, and the removal efficiency is not sufficient.
In another mechanical coated layer peeling method, the resin product is crushed to fine particles and is heated to melt it. Then the melt is filtered by using a sieve, thereby the coated layer pieces being removed, this being a screen mesh method. In this method, the non-toxicity and the environmental stability are its merits, but the screen meshes are frequently clogged. Therefore, there is the disadvantage that the screen mesh has to be replaced very frequently, thereby lowering the productivity.
Now the chemical coated layer peeling methods will be described. These chemical methods are effective in removing the coated layer in the curved and depressed portions, but in these methods, a secondary treatment such as the treatment of waste water is accompanied. Further, the overall treating efficiency is low.
To describe them specifically, Japanese patent 93-93157 (entitled "COATED LAYER PEELING METHOD, AND POST TREATMENT"), 93-9420, and 93-9419 are known to be most effective among the chemical methods. In these methods, the coated layer is removed by using a mixture of a biprotonic solution, alcohol, and a metal or quarterly ammonium thio-cyanate. In this method, the ether bonds near the bridge point of the coated resin is cut by using an organic salt, thereby decomposing the coated layer material.
However, this method uses halogenic organic solvents such as chloro-penta-fluoro-propane, methylene chloride, chloroform, and tetra-carbon chloride. These solvents are likely to destroy the ozone layer, and may be harmful to the workers. Therefore it is proposed that these halogenic organic solvents be substituted with other chemical materials.
However, even if the toxicity to the human health and the environmental pollution are slightly improved by the substitution, the danger remains all the same. Further, in peeling the coated layer, the peeling process and the filtering process are very much complicated, and the mixing ratio of the chemicals has to be adjusted very often. Further, an auxiliary facility is required to recover and purify the chemicals to recycle them. These are the major problems of this method.
Another chemical method is disclosed in Japanese Patent 93-115810 (entitled "METHOD FOR REGENERATING COATED PROPYLENE RESIN BUMPER"), and Japanese Patent 93-115811. In these methods, the resin product is crushed, and then, surfactants such as a fatty acid slat, fatty acid sugar ester, fatty acid sorbitan ester, alkyl benzene sulfonate and the like are added to peel off the coated layer.
In this technique, the toxicity to the human health and the harm to the environment are low, but the secondary treatment has to be gone through, in addition to the fact that the treatment efficiency is low.
As another chemical method, there are Japanese Patents 94-107983 and 93-220440 (in which aqueous alkaline solution is used, and heating is carried out to a high temperature), Japanese Patent 94-99433 (in which alcohol, water, amine or azoles are used), and Japanese Patent 93-84746 (in which methylene chloride and water are used). In these methods, a post treatment is required, and therefore, the facility cost and the time extension are excessive. Further, the efficiency is low, and the toxicity to the human body and the environmental safety are problematic.
As another chemical method, there are Japanese Patents 95-108532 and 94-285858 in which the chemicals are replaced with water so as to carry out hydrolysis.
In this hydrolysis method, the toxicity and the environmental contamination can be solved. However, if the treatment time is to be shortened, and if the peeling efficiency is to be improved, acid, alkali or alcohol has to be added. If chemicals are not used, the treatment time is extended. Further, if the peeling efficiency is to be improved, a high temperature and a high pressure have to be applied.
To review the above described mechanical and chemical methods, the mechanical methods such as shot-blast method and the vibration compression method lack economy, and are not suitable for products of complicated contours.
In the mechanical methods, too many process steps are required, the treatment time is long, and the peeling efficiency is low, although they have merits such as a low environmental pollution and a low cost.
The chemical methods include the hydrolysis method, the alkali dissolving method, and the organic salt method, which have been put the practical use. In these methods, however, the organic solvents have to be heated up to the boiling points, and therefore, the process becomes unstable, while the costs for the recovering facility and the post treatment are excessive.
Further, the workers may be exposed to the toxicity, and the environment may be contaminated.
Currently, the automobile makers are trying to combine the advantages of the mechanical and chemical methods, but no tangible result has been reaped so far.
In the conventional methods as described above, the coated layer can be peeled off only after crushing the coated bumper, and therefore, the peeling efficiency is low. Further, the bulk of the peeling facility is large, and therefore, the installation area becomes large, as well as requiring a high operating cost.
Further, after the completion of the peeling process, the coated layer pieces still remain, and therefore, a complicated secondary treatment process such as filtering and water discharging is required. Due to this secondary treatment process, the treatment time and the treatment cost become excessive, thereby causing a problem.
Meanwhile, in the chemical methods, the problems are the toxicity to the human body and the environmental contamination.